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About the Type A UPC

The basic UPC code, referred to as Type A, is composed of twelve digits.
These twelve digits are broken up into the four groups described below:

Number System Character (NSC)

The first digit represents the 'number system' of the UPC code. Most
'normal' products use number system zero (0), but several other number
systems are also in use.

Manufacturer Code

The next five digits represent a 'manufacturer code.' Manufacturer codes
are given out by the Uniform Code Council (UCC).

Product Code

The next five digits correspond to a specific product, and are issued by
the manufacturer of the product. The meaning of these numbers are different
for the UPC codes used on coupons.

Check Digit

The last digit is used to check the integrity of the other digits in the
number. The calculation is relatively simple.

Calculating the Check Digit

Assume the Number System Character is 'A', the
Mfr Code is 'BCDEF', and the Product Code is 'GHIJK'. Calculate A + C + E
+ G + I + K, multiply that by 3, then add B + D + F + H + J. The check
digit is how much you have to add to that number to make it a multiple of ten.

An example: The UPC 04042100192X, where X is the check digit that we don't
know. We calculate (0 + 0 + 2 + 0 + 1 + 2) * 3 + (4 + 4 + 1 + 0 + 9) = 33.
The check digit (X) is then 7, since we can add 7 to 33 and get a multiple of
ten (40).